This invention relates to a multifocal non-achromatized or achromatized multicomponent optical lens system and, more particularly, to such a system wherein at least one of the lens components is a birefringent lens.
Birefringent lenses have been known for some time. U.K. Patent No. 231,848 describes a birefringent lens which is used as a polarizer. Since a birefringent lens produces two orthogonally polarized light beams of different vergence, either a diaphragm or an isotropic lens is employed to eliminate one of the two polarized beams in order to provide a beam of one type of polarization only. U.S. Pat. No. 2,317,809 features a plano-convex birefringent lens cemented upon its convex side to a planoconcave isotropic lens. The assembly acts as a lens with positive power for light of one state of linear polarization and as a parallel plate with zero optical power for light of the other, orthogonal state of polarization. The lens assembly is integrated in a finder for photographic purposes. In U.K. Patent No. 865,361, a prismatic birefringent lens is combined with an isotropic cover lens in such a way that the two powers of the combination of lenses are equidistant from the target power. The lens system is incorporated in optical apparatus for testing the human eye. The apparatus separates the two images formed by the o- and e-rays so that two images of different degrees of acuteness can be viewed simultaneously and side-by-side during eye examination. U.S. Pat. No. 3,211,048 makes mention of plano-convex/plano-concave doublet lens assemblies made of identical birefringent materials. In the assemblies, one of the two birefringent lenses may be replaced by an isotropic lens with a plane surface. The assemblies work in concert with a dispersive device, e.g., a prism, and a polarizer in a spectrometer. U.S. Pat. No. 3,432,238 also discloses doublets of plano-concave/planoconvex birefringent lenses for the production of phase shifts of incident polarized light. The resultant interference patterns are utilized in a spectrometric apparatus.
Since a birefringent lens has one power associated with one plane of linear polarization and another power with the other, orthogonal plane of polarization, means which are able to rotate the plane of polarization can be used to select one of the two powers if the incoming light is linearly polarized. U.S. Pat. No. 3,410,624 uses electro-optic control means (a Kerr cell) together with birefringent lenses and prisms. It is disclosed in this patent that m systems comprising each a lens and an electro-optic cell can produce 2.sup.m focal points. A similar assembly of n electro-optic cells and n birefringent lenses is disclosed in French Patent No. 1552198. U.S. Pat. No. 3,520,592 and Eng. et al., "Multiple Imagery with Birefringent Lenses", Applied Optics, Vol. 8, No. 10, pp. 2117-2120 (Oct., 1969) each disclose an optical focusing system using one or more birefringent lenses, each lens combined with a control device for the polarization plane of light. U.S. Pat. No. 3,563,632 discloses a digital optical focal length modulator in which an assembly of aligned successive stages, each possessing a Kerr cell and a birefringent lens of progressive curvature, is immersed in a common electrolytic tank. The lenses are shaped such that the temperature-dependence of the refractive index of the electrolyte is compensated. U.S. Pat. No. 3,565,510 discloses the use of two birefringent lenses per Kerr cell in a system analogous to that mentioned in aforesaid U.S. Pat. No. 3,563,632. Osipov, "Binary polarizing lenses", Optical Technology, Vol. 40, No. 5, pp. 277-279 (May, 1973) describes a binary polarizing lens consisting of a plano-convex/plano-concave birefringent lens system. This lens system may be combined with an isotropic lens in order to produce a parallel reference beam and a focused signal beam, the beams being polarized orthogonally, for use in laser systems. U.S. Pat. No. 3,758,201 discloses a plano-convex/plano-concave variable power lens system. The system is used in eye examination. U.S. Pat. No. 3,990,798 discloses a plano-convex/plano-concave birefringent lens doublet for use as, or in, an eyepiece of a microscope in order to produce the images of objects within different object planes in a single image plane. Plano-convex/plano-concave doublet lenses made of birefringent material are also disclosed in U.S. Pat. No. 4,566,762 describing a dual focus system in which the images of differently distant objects exhibit identical magnification. U.S. Pat. No. 4,575,849 discloses plano-convex/plano-concave birefringent lenses which are used as phase-plates in an optical filter-polarizer combination.
It appears from the foregoing that birefringent lenses have been used primarily in plano-convex/plano-concave lens assemblies. Such an assembly is combined in one instance, i.e., in Osipov, with an isotropic lens in order to produce a parallel beam of polarized light. A combination of a prismatic birefringent and a prismatic isotropic lens is used in U.K. Patent No. 865,361, supra, to produce two side by side images of one object for the purpose of eye examination. Furthermore, assemblies of systems, each system incorporating a birefringent lens and a control means for the orientation of the polarization plane have been suggested as variable focal distance systems in various patents.
In the above-mentioned prior disclosures inorganic crystals such as quartz and calcite are mentioned as birefringent lens materials. Birefringence can also be a property of some kinds of organic polymers. Thus, for example, U.S. Pat. Nos. 4,384,107; 4,393,194; 4,933,196; 4,433,132; 4,446,305; 4,461,886; 4,461,887; 4,503,248; 4,520,189; 4,521,588; 4,525,413; 4,575,547; 4,608,429; and, 4,628,125 describe polymers which exhibit high birefringence and simulate the optical properties of uniaxial crystals. Such birefringent polymers are proposed for use with isotropic layers in multilayer light transmitting and polarizing devices.
The fact that many polymers can be birefringent by, e.g., applying stress is known. The entire field of photo-elasticity and stress analysis by means of polarized light is based on this phenomenon. It is also known that by stretching a polymer beyond its elastic range, birefringence can be imparted to the polymer irreversibly. Mention of this is made, e.g., in U.S. Pat. No. 3,522,985.
Ophthalmic lenses having multiple foci and, in particular, contact lenses possessing this property are known, e.g., from U.S. Pat. Nos. 3,794,414; 4,162,122; 4,210,391; 4,340,283; 4,338,005; 4,637,697; 4,641,934; 4,642,112; and, 4,655,565. It is common to these lenses that the optical media employed in their fabrication are isotropic. The simultaneous multipower features are achieved by providing the lens with appropriate geometrical parameters.